Electron tube circuits



Feb. 14, 1950 P. N. MARTIN ELECTRON TUBE CIRCUIT Filed Aug. 6, 1948 1 l-J LB rlight Beam INVENTOR. Pau MMaPtin BY j HIS ATTORNEY atented Feb.i4, 550

ELECTRON TUBE CIRCUITS Paul N. Martin, Penn Township, Allegheny County,Pa., a'ssignor to The Union Switch & Signal Company, Swissvale, Pa., acorporation of Pennsylvania Application August 6, 1948, Serial No.42,833,

11 Claims.

My invention relates to electron tube circuits and particularly toelectron tube circuits employing gas tubes of the grid-controlled type.

It is well known in the art that grid-controlled gas tubes have theinherent property of remaining conductive after being fired until theanode potential is reduced to a value below the deionizing voltage ofthe tube. That is, if sufficientpotential is supplied to the anode ofthe tube, the tube will remain non-conductive as long as the controlgrid has a sufiicient negative potential supplied thereto to preventionization from starting, but when the grid potential becomes lessnegative or becomes positive, the tube fires and the grid loses control.When alternating current is supplied to the anode of the tube, the tubecan only fire on the alternate half-cycles in which the anode ispositive with respect to the cathode, so that the tube is extinguishedwithin one-half cycle after the grid is driven negative, and accordinglythere is no diificulty in stopping the conduction of the tube in orderthat the grid may regain control.

However, if the anode is supplied with direct current energy, means mustbe provided to interrupt or materially reduce the current supplied tothe anode circuit after the tube is fired in order for the grid toregain control of the tube. It has previously been proposed to provide agas tube circuit for controlling a relay, in which short pulses ofpositive potential are supplied recurrently to the grid of a gas tube,the anode circuit of which is supplied with direct current, by providinga relay having its winding and one of its back contacts connected inseries in the anode circuit so that when the tube fires on the receptionof a pulse of voltage by its grid circuit, the relay will pick up andits back contact will interrupt the series anode circuit, whereby thetube is deionized and the relay released. When the contacts of the relayrelease, the series anode circuit is again established, but the tube isthen deionized and under the control of its grid, so that the tube doesnot fire until another pulse drives the grid in a positive direction.Although this arrangement provides for stopping the conduction of thetube, it cannot be relied upon in the event ofa fault. For example, ifthe anode and the cathode of the tube becomes short circuited, or if thecontrol grid bias is lost so that the tube fires each time the anodecircuit is closed, the relay in the anode circuit will recurrently pickup its contacts in a manner of doorbell operation, and the period of theoperation might be the same as that of its normal operation, in whichcase the operation of the relay in the absence of the control voltagewould be the same as if it were under control of the voltage normallysupplied to the grid of the tube. This may be considered as an unsafefailure.

The object of my invention is to provide an improved system of electrontube circuits for use with a gas-filled electron discharge device havinga direct current anode supply, which system is adapted for use in asafety system embodying the closed circuit principle of operation.

More particularly, the object of my invention is to provide an improvedsystem of electron tube circuits for operating a relay periodically inresponse to successive pulses of control energy sup-' plied to a grid ofa gas tube havingits anode circuit supplied with direct current energy,which is so arranged as to prevent improper periodic operation of therelay in the event of a fault in the system.

Another object of my invention is the provi sion of an improvedphotocell detector system which ,is operable from a local direct currentsource, for the purpose of detecting the presence of an object within aprotected area in a reliable manner.

Other objects of my invention and features of novelty therein will beapparent from the following description, taken in connection with the accompanying drawing.

In practicing my invention, I provide a gas tube having an anode, acathode, and a control electrode, of the type in which the anode circuitis rendered conductive by the brief application of a positive potentialto the control electrode, the anode circuit then remaining conductiveuntil the anode voltage is reduced below a predetermined 'value. Thecontrol electrode is normally biased in a negative direction, to therebyrender the tube normally non-conductive. The control electrode of thetube is recurrently sup- .plied with pulses of control voltage having avalue suificient to overcome the bias and render the tube conductive.The anode circuit of the tube has in series therewith the winding of acontrol relay, and the parts are proportioned and arranged so that therelay picks up when the tube is rendered conductive. A shunting circuitis provided which includes a front contact of the control relay, b whichthe anode and cathode of the tube are connected together, orshort-circuited, when the relay picks up. The shunting circuit alsoconstitutes a stick circuit for the relay, so that each time the tube isrendered conductive by a control pulse the relay .picks up and is heldenergized over its stick circuit which short-circuits the anode-cathodecircuit of the tube to cause it to become deionized.

In order to restore the apparatus to its original condition when thecontrol voltage ceases to be supplied, I provide a second relay which isarranged to interrupt the shunting circuit after a short time interval,so that the control relay will release, provided the anode-cathodecircuit in series with the relay has returned to its normalnon-conducting state.

I shall describe one form of electron tube circuits embodying myinvention and shall then point out the novel features thereof in claims.

The accompanying drawing shows a preferred embodiment of my invention asapplied to an intrusion detection system employing an interrupted lightbeam and a photocell.

It is to be understood that my invention is not limited to use inphotocell systems, but that it may be advantageously used in othersystems involving the detection of recurrent electrical pulses of lowenergy.

Referring to the accompanying drawing, an intrusion detection system isshown which serves to detect the presence of an object within aprotected area PA by the interruption of a light beam which isrecurrently projected across the area PA to activate a photo-electriccell.

The light source LS includes an electric lamp EL which is recurrentlysupplied with energy from a low voltage direct current source, notshown, the positive and negative terminals of which are designated bythe reference characters B and C,

respectively. The supply of energy to the lamp EL is governed by acontact 5 of a code transmitter CT. Such code transmitters are wellknown in the railway signaling art, and it will sufiice to point outthat the code transmitter CT has its operating winding continuouslyconnected to the low voltage source, and is constructed and arranged torecurrently open and close its contact 5 at some predetermined rate,say, for example, 180 times per minute.

Accordingly, the lamp EL of the light source LSis recurrentlyenergized-180 times per minute and the flashes of light generatedtherebyare projected-by a lens system, not shown, as a recurrently interruptedlight beam across the protected area PAto photocell PC, as long asthespace PA is not occupied. I

The apparatus for detecting the recurrent flashes of light comprises thephotocell PC, a gas tube VT, a first relay ER; a second relay EPR, andcode-detecting means comprising two slow release relays FSA and BSA.

Energy for the operation of the photocell PC and gas tube VT is suppliedfrom a high voltage direct current source, not shown, the positiveterminal of which is designated by the referencecharacter-s BH, and thenegativeterminal of which is grounded.

The anode I of the photocell PC is supplied with positive direct currentenergy at a suitable value by an adjustable tap 9 of the voltage dividerVD, which comprises a suitable'resistance connected between terminal BHand ground. The cathode I l of photocell PC is connected togroundthrough a load resistor RI, and the photocell PC is of the type inwhich the amount of conduction is dependent upon the intensity of thelight falling upon the photo-sensitive portions of the cell.

The adjustable tap 9 of voltage divider VD provides a means foradjustingthe sensitivity of the photocellPC, so that it may be adjustedto operate at maximum efiiciency.

When the recurrently interrupted light beam LB strikes the photocell PCthe conductionof the cell is increased, and the flow of currenttherethrough and through the load resistor RI increases proportionally.The flow of current through the resistor RI causes a voltagedrop, whichis suppliedto the control electrode or grid I3 of gas tube VT, through acoupling condenser CI, and a protective resistor R2.

The cathode I5 of the gas tube VT is connected to an adjustable tap llof the voltage divider VD, while the grid I3 of gas tube VT is connectedto ground through the resistor R2 and a grid bias resistor R3.Accordingly, it will be seen that the cathode I5 of gas tube VT ismaintained at a slightly positive potential with respect to ground bythe connection to voltage divider VD through the adjustable tap ll,while the grid I3 of the tube VT is connected to ground through theresistors R2 and. R3. Thus the cathode I5 is slightly positive inpotential with respect to the grid I3 or conversely, the grid I3 has agiven negative bias with respect to the cathode [5 of the tube.

The anode I9 of tube VT is supplied with energy from the positiveterminal Bi-I of the high voltage direct current source through awinding of a relay ER, while as previously pointed out the cathode I5 isconnected to ground through a portion of the voltage divider VD by theadjustable tap H. The potential between the anode I9 and the cathode I5of tube VT is such that it is sufilcient to cause the tube to conductwhen the grid I3 is driven in a positive direction. The apparatus isarranged and proportioned so that the Value of negative grid biassupplied to the grid I3 of the, tube is sufii'cient to prevent the tubefrom conducting, but when an impulse of control voltage is supplied tothe grid I3 from the load resistor RI as a result of the reception oflight on the photocell'PC, the grid I3 is driven sufiiciently positivewith respect to cathode I5 to allowth tube to conduct.

From the foregoing, it will be seen that when a positive pulse of energyis supplied to the control grid I3 of gas tube VT, as a result of thelight beam striking the photocell PC, the tube VT will berenderedconductive, and the current which flows through the Winding of relay ERwill cause the relay to pick up its contacts. When contact 2I of relayER picks up, it establishes a circuit for connecting the anode I9 oftube VT to the cathode I5, and which circuit is completed-over a backcontact 23 of relay EPR. As a result, the anode I9 and cathode I5 oftube VT are established at the same potential, and the tube will bedeionized. The relay ER will remain picked up at this time however,since energy now flows through the winding of the relay ER, over frontcontact 2| of the relay, over back contact 23 of relay EPR, to theadjustable tap I! on the voltage divider VD and to ground.

When contact 25, of relay ER picks up, it establishes a'circuit forenergizing the winding of relay EPR, which is traced from termina-l'iBof the low voltage source, over front contact '25 of relay ER, throughthe winding of EPR, and over back contact 21 of relay- EPR to terminalC. When relay EPR'picks up, its back contact?! interrupts the circuitfor connecting its winding to terminal C," but the relay remainsenergized due to the flow of energy through its winding from condenserC2, condenser C2 having been charged from the low voltage source throughback contact 21 of relay EPR and then connected across the winding ofthe relay EPR through front contact 25 of relay ER; Accordingly, it willbe seen that when relay ER picks up, the relay EPR will pick up shortlythereafter, and will remain picked up for a short interval dueto thecharge on condenser C2.

When contact 23 of relay EPRpicks up; it

interrupts the circuit previously traced for connecting the anode I9 andthe cathode [5 of tube VT and also for maintaining the relay ER pickedup by its stick circuit. The tube VT being now deionized so thatconduction no longer takes place between the anode l9 and the cathodeI5, the relay ER releases, and its contacts 2| and 2 5 open. Whencontact 25 of relay ER opens, it interrupts the circuit for supplyingenergy to the winding of relay EPR from the condenser C2 and relay EPRreleases, thus restoring the equipment to its original condition.

It will be apparent that successive pulses of energy supplied to thegrid of the gas tube VT will cause the operation described above to berepeated for each pulse.

The contacts of the code transmitter CT and the contacts of relays ERand EPR are shown by a downwardly inclined heavy line indicating oneposition of the movable contact and a horizontal dotted line indicatingthe other position of the movable contact, such a showing beingwellknown in the railway signaling art for designating contacts whichmay be recurrently operated between their two positions.

The recurrent operation of the contacts of relay ER is detected bycode-detecting means including the slow release relays FSA and BSA. Whenrelay ER picks up, its front contact 29 establishes an obvious circuitfor supplying energy to the winding of relay FSA, and relay FSA picksup. When relay ER releases its contacts, a circuit is established forsupplying energy to the winding of relay BSA which includes back contact28 of relay ER and front contact 3| of relay FSA. Accordingly, energywill be supplied to relay FSA each time that contact 29 of relay ER ispicked up, and energy will be supplied to the winding of relay BSA whencontact 29 of relay ER is released, provided that contact 3| of relayFSA is picked up. Relays FSA and BSA are slow releasing and remainpicked up when contact 29 is operated at a rate corresponding to thegiven rate of the impulses applied to gas tube VT. The contact 33 ofrelay BSA may be used to control various circuits, for example, signalcontrol circuits for governing trafiic movements into the protected areaPA. It will be seen that if the recurrent operation of contact '29ceases, the supply of energy to one or the other of the relays FSA andBSA will be cut off. As a result, the contact 33 of relay BSA will bereleased, thereby interrupting circuits controlled by that contact.

It will be apparent to those skilled in the art that my invention is notlimited to the code detecting means shown and described, but that anysuitable means for detecting the recurrent operation of a contact orcontacts may be employed, such as, for example, the arrangement shownand described in Letters Patent of the United States No. 2,237,788,granted to Frank H. Nicholson et al.

Normally, with the protected area PA unoccupied, the recurrent flashesof light projected across the area by the light Source LS to thephotocell PC cause the recurrent operation of contact 29 of relay ER,with the result that relays FSA and BSA are picked up, and contact 33 ofrelay BSA maintains the circuit controlled thereby.

When the protected area PA is occupied, the light no longer is suppliedto the photocell PC and as a result, relay ER releases and remainsreleased, so that relays FSA and BSA release.

6 Contact 33 of relay BSA interrupts the circuits governed thereby, toindicate that the protected area PA is occupied.

When the protected area PA again is unoccupied, the light beam LB againstrikes the photocell PC, with consequent operation of relay ER, andrelays FSA and BSA are picked up, with contact 33 of relay BSA againestablishing the circuit controlled thereby.

From the foregoing, it will be seen that my invention provides electrontube apparatus in which recurrent pulses of control energy supplied to acontrol electrode of the gas tube causes the tube to become conductiveto thereby energize the relay. When the relay picks up, it establishes acircuit for causing the tube to be deionized, and also governs means forrestoring the relay to its original condition. The recurrent operationof the contacts of the first relay governed by this tube, in this caserelay ER, is detected by means of conventional code-detecting equipment.

As previously pointed out, it is essential that equipment of this typeis arranged to insure that faulty operation cannot occur as a result ofa failure of the tube or other derangement of the apparatus.

For example, ii the tube VT has its anode l9 and cathode l5short-circuited internally or otherwise or if a derangement otherwiseoccurs which causes the tube to continuously fire, it will be seen thatthe relay ER will be picked up and remain picked up, due to thecontinuous current through the tube. Since contact 25 of relay ERremains in its picked up position, the circuit for supplying energy tothe winding of relay EPR is maintained, but back contact 2'! of relayEPR causes the relay to interrupt its pick-up circuit each time that itpicks up, so that after the release time determined by the charge ofcondenser C2, the relay EPR will release. Accordingly, it will be seenthat the contacts of relay EPR will recurrently pick up and release in adoorbell fashion, and each time that contact 23 of relay EPR picks up itinterrupts the circuit including front contact 21 of relay ER forquenching the tube. However, if the tube is continuously conducting orotherwise maintains a continuous path therethrough, the relay ER willremain steadily energized. When contact 7.9 of relay ER remains pickedup, the supply of energy to the winding of relay FSA is continued, butthe supply of energy to the winding of relay BSA is interruped bycontact 29 of relay ER, so that after the release time of relay BSA hasexpired, its contact 33 will release and interrupt the circuitscontrolled thereby. Thus the apparatus will operate in the same manneras if the light beam LB were interrupted by an object occupying theprotected area PA, and this type of failure is on the side of safety.

The relay EPR with its back contact 21 interposed in the circuit forsupplying energy thereto from the source, has another function, namely,that of protecting the equipment against false operations caused bytransient voltages supplied to the grid l3 of the tube VT.

It will be assumed that relay ER has picked up as a result of the supplyof a pulse of control energy to the grid 13 of the tube VT, and that thetube VT has now been deionized and the relay ER is about to release. Ifa pulse of transient voltage is supplied to the grid (3 of the tube atthis time, it will cause the tube to again become conductive and relayER will continue to be picked up. However, relay EPR will release due toits estatesback contact 21 opening the circuit for supply ng energy. tothe winding of the .relay, and when back contact 23 of relay EPRreleases, it establ-ishes the circuit for shunting the plate, andcathode of the tube VT, so that the tube is again deionized.Accordingly, with the circuit arranged in accordance with my invention,a transient voltagev appearing at the grid !3 of gas tube VT just at atime that the relay ER is aboutto release its contacts would not lockupthe relays and prevent further operation.

' From the foregoing it will be seen that I have provided an electrontube circuit arranged for utilizing a gas type tube supplied with energyfrom a direct current source, and the arrangement is such that possibleunsafe failures of the equipment are guarded against.

Although my invention is especially suited for use with electron tubecircuits'of the type described employing direct current energy, it is tobe understood that the arrangement is equally suitable for use withalternating current energy. Likewise, it is to be understood that thearrangementof relay control circuits is not limited to that shown on thedrawings, and other arrangements of these circuits may be provided ifdesired.

Although I have herein shown and described only-one'form of apparatusembodyin my invention, it is to be understood that various changes andmodifications therein may be made within the scope'of the appendedclaims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1.In combination, a source :of direct current, an electron dischargedevice supplied with current from said source, said device having ananode-cathode circuit which is rendered conductive by the application ofa control voltage and which remains conductive when said voltage isreduced, as long as current is supplied thereto from said source, meansfor applying va control voltage to said device to render said circuitconductive, .a first relay having its winding connected in series withsaid circuit to the terminals of said source, said relay assuming itsenergized position when said circuit becomes conductive, means includinga front contact of said relay for shortcircuitin said anode-cathodecircuit to render saiddevice non-conductive without releasin said relay,andmeans including a contact of a second relay controlled by said relayfor removing said short circuit after said first relay has .been pickedup for-a time interval long enough to'enable said device to change fromits conductive to its nonconductive state.

, 2. In combination, a source of direct current, an electron dischargedevice supplied with current from said source, said device having ananode-cathode circuit which is rendered conductive by the application ofa control voltage and which remains conductive when said voltage ,isreduced, as long as current is supplied thereto from said source, .meansfor applying a control voltage to said device to render said deviceconductive, a first relay having its winding connected in series withsaid circuit to the terminals of said source, said first relay assumingits energized position when said circuit becomes conductive, meansincluding a front contact of said relay for -'short-circuiting saidanode-cathode circuit without releasing said relay, and means including:a contact of va second relay controlled by said first relay whenenergized I-for periodically interrupting said short circuit, theintervalbe tween such interruptions being greater than the time requiredfor said device to change from, its conductive to its non-conductivestate.

3. An electron tube circuit comprising an electron tube having an anode,a cathode and a control electrode, a source of direct current connectedacross said anode and said cathode and having in series therewith awinding of a first relay, said source and said tube being proportionedso that the voltage supplied to the tube from the source is sufiicientto render said tube conductive, means for supplying biasing voltage tothe control electrode of said tube to render the tube normallynon-conductive, means for at times supplying recurrent voltage pulses tosaid control electrode of suificient value to overcome said biasingvoltage and thereby render the tubeconductive, a

second relay governed by a front contact of said,

first relay, and a circuit for shunting the anode and cathode of saidtube and including a front contact of said first relay and a backcontact of said second relay in series.

4. An electron tube circuit comprising an electron tube having an anode,a cathode, and a control electrode, a source of direct current connectedacross said anode and said cathode and having in series therewith awinding of a first relay, said source and said tube being proportionedso that the voltage supplied to the tube from the source is sufficientto render said tube conductive, means for supplying biasing voltage tothe control electrode of said tube to render the tube normallynon-conductive, a control voltage source for at times supplying voltagepulses to said control electrode, said pulses being of sufiicient valueto overcome said biasing voltage and thereby render the tube conductive,a slow release relay, a circuit for said slow release relay including afront contact of said first relay and its own back contact, and acircuit for shunting the anode and cathode of said tube includin a frontcontact of said first relay and a back contact of said slow releaserelay.

5. In combination, a gas tube having an anode,-

a cathode and a control electrode, a source of direct current connectedacross said anode and said cathode and having in series therewith awinding of a first relay, said source and said tube; being proportionedso that the voltage supplied to the tube from the source is sufllcientto render said tube conductive, means for supplying biasing voltage tothe control electrode of said tube to render the tube normallynon-conductive, a control voltage source for at times supplying voltageto said control electrode of value sufficient to overcome said biasingvoltage and thereby render the tube conductive, a, second relay, acircuit for said second relay including its own back contact and a frontcontact of said first relay, and a circuit for shuntin the anode andcathode of said tube including a front contact of said first relay and aback contact of said second relay.

6. In combination, an electron tube of the gas filled type having ananode, a cathode, and a control electrode, a source of direct currentfor supplying a positive Voltage to said anode, means for supplying abiasing voltage to the control :elec-- trode of said tube, a source ofcontrol voltage for supplying recurrent pulses to the control electrodeof said tube, said tube being rendered conductive ductive, means forrendering said tube non-com ductive each time said first relay becomesenergized comprising a second relay governed by a front contact of saidfirst relay and a circuit for connecting the anode to the cathode ofsaid tube which includes a front contact of said first relay and a backcontact of said second relay, and means for distinctively indicating therecurrent operation of said first relay.

'7. An electron tube circuit comprising an electron tube of the gasfilled type having an anode, a cathode and a control electrode, a sourceof direct current anode voltage sufficient to render said tubeconductive, means for supplying a biasing voltage to said controlelectrode to prevent said tube from conductinga source of recurrentpulses of control voltage having a value sufiicient to overcome saidbiasin voltage and thereby render said tube conductive, means forsupplying said pulses recurrently to said control electrode, a firstrelay having its winding connected in series with said anode and saiddirect current source, said first relay assuming its energized positionwhen said tube is rendered conducting, a second relay, a circuit forsaid second relay including a front contact of said first relay and itsown back contact, a circuit for connecting the anode and cathode of saidtube together including a front contact of said first relay and a backcontact of said second relay, a slow release relay controlled over afront contact of said first relay. a detector relay, a circuit forsaiddetector relay including a back contact of said first relay and afront contact of said slow release. relay whereby said detector relay ismaintained energized only in response to the recurrent operation of saidfirst relay.

8. An electron tube circuit comprising an electron tube having an anodeelectrode, a cathode electrode, and a control electrode, a source ofenergy connected across said anode and said cathode and having in seriestherewith a winding of a first relay, said first relay being arrangedand proportioned so that its contacts are operated from a first to asecond position when said tube is rendered conductive, said source andsaid tube being proportioned so that the voltage supplied to the tubefrom the source is sufiicient to render said tube conductive, means forsupplying biasing voltage to the control electrode of said tube torender the tube normally non-conductive, means for at times supplyingrecurrent voltage pulses to said control electrode of sufiicient valueto overcome said biasing voltage and thereby render the tube conductive,a second relay governed by a second position contact of said firstrelayiland having contacts operated from a first to a second positionwhen energy is supplied to the winding of the relay, a "circuitincluding a second position contact of said first relay and a firstposition contact of said'second relay, for connecting .-together two ofsaid electrodes of said tube to thereby render the tube non-conducting,and a stick circuit including a second position contact of said firstrelay and a contact of said second relay closed in its first positionfor retaining said first relay in its second position for a short timeinterval after said tube is rendered non-conducting.

9. An electron tube circuit comprising an electron tube having an anodeelectrode, a cathode electrode, and a control electrode, a source ofenergy connected across said anode and said oathode and having in seriestherewith a winding of a first relay, said first relay being arrangedand proportioned so that its contacts are operated from a first to asecond position when said tube is rendered conductive, said source andsaid tube being proportioned so that the voltage supplied to the tubefrom the source is sufiicient to render said tube conductive, means forsupplying biasing voltage to the control electrode of said tube torender the tube normally non-conductive, means for at times supplyingrecurrent voltage pulses to said control electrode of sufiicient valueto overcome said biasing voltage and thereby render the tube conductive,a second relay governed by a second position contact of said firstrelay, a shunting circuit including a contact of said first relay closedin its second position for rendering said tube non-conductive, saidshunting circuit including a contact of said second relay for openingsaid shunting circuit, and a stick circuit for maintaining said firstrelay in its second position for a short time interval after said tubestops conducting, said stick circuit including a second position contactof said first relay and a contact of said second relay.

10. An electron tube circuit comprising an electron tube having an anodeelectrode, a cathode electrode, and a control electrode, a source ofenergy connected across said anode and said cathode and having in seriestherewith a winding of a first relay, said first relay being arrangedand proportioned so that its contacts are operated from a first to asecond position when said tube is rendered conductive, said source andsaid tube being proportioned so that the voltage supplied to the tubefrom the source is sufiicient to render said tube conductive, means forsupplying biasing voltage to the control electrode of said tube torender the tube normally non-conductive, means for at times supplyingrecurrent voltage pulses to said control electrode of sufiicient valueto overcome said biasing voltage and thereby render the tube conductive,a second relay governed by a second position contact of said firstrelay, a first circuit including a contact of said first relay forstopping the conduction of said tube, a stick circuit for maintainingsaid first relay in its second position, and means including contacts ofsaid second relay for opening said first circuit and said stick circuitafter a short time interval following the operation of said first relayto its second position.

11.' In combination, a gas tube having an anode, a cathode and a controlelectrode, a source of direct current, a relay, an anode-cathode circuitincluding in series said source, the anode-cathode tube ;space of saidtube and a winding of said relay, said relay being energized and fpickedup in response to the current flowing in the anodecathode circuit whensaid tube is ionized, means including a source of control voltageconnected to said control electrode to at times apply a voltage thationizes said tube, and a circuit path including a contact of said relayclosed when said relay is energized to short-circuit the anode andcathode of said tube to enable the tube to change from its ionized toits deionized condition subsequent to the application of said controlvoltage. PAUL N. MARTIN.

No references cited.

